virtio: fix vhost handling

Commit b1f416aa8d870fab71030abc9401cfc77b948e8e breaks vhost_net
because it always registers the virtio_pci_host_notifier_read() handler
function on the ioeventfd, even when vhost_net.ko is using the ioeventfd.
The result is both QEMU and vhost_net.ko polling on the same eventfd
and the virtio_net.ko guest driver seeing inconsistent results:

  # ifconfig eth0 192.168.0.1 netmask 255.255.255.0
  virtio_net virtio0: output:id 0 is not a head!

To fix this, proceed the same as we do for irqfd: add a parameter to
virtio_queue_set_host_notifier_fd_handler and in that case only set
the notifier, not the handler.

Cc: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Tested-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/hw/virtio.c b/hw/virtio.c
index d146f86f13..209c763751 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -1021,13 +1021,16 @@ static void virtio_queue_host_notifier_read(EventNotifier *n)
     }
 }
 
-void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign)
+void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
+                                               bool set_handler)
 {
-    if (assign) {
+    if (assign && set_handler) {
         event_notifier_set_handler(&vq->host_notifier,
                                    virtio_queue_host_notifier_read);
     } else {
         event_notifier_set_handler(&vq->host_notifier, NULL);
+    }
+    if (!assign) {
         /* Test and clear notifier before after disabling event,
          * in case poll callback didn't have time to run. */
         virtio_queue_host_notifier_read(&vq->host_notifier);